WOFF FM Thread

[+gavagai]

Maybe that was why the RNAS Camels had 150hp Bentley rotaries....  (Which, being made in England was about half the price). 

 

The 130hp Clerget was license built in the UK.  It was the license that made them expensive.  The license built engines were notorious by the Fall of 1917 in Camel squadrons.  French made Clergets were much better.

 

 

Notice that one of the brand new license-built engines was worse than a French engine with 64 hours of wear.

[Bucksnort]

The 130hp Clerget was license built in the UK.  It was the license that made them expensive.  The license built engines were notorious by the Fall of 1917 in Camel squadrons.  French made Clergets were much better.

 

Gav,

 

So you're thinking the approx 150 Sopwith Triplanes built had a French made Clerget which would have been better...which makes sense.  Then the numbers in my post of the RFC test might be valid.  If I put the Triplane at a top speed of 117 sea level then it would be faster than the early Alb D.III's but on parity with the OAW and slower than the Alb D.V (I sped up the OAW D.III to 117 at sea level to represent the later/faster D.III's as it is the last D.III that appears in the game and I found ratings of 117-118 mph at sea level on the later D.III's with the new spinner design and larger engines).  I just read another article last night about the Triplane being withdrawn in late 1917 due to being outclassed in performance and firepower, so running it at 117 mph sea level might be a good fit then.  That way it has its heyday in the first half of 1917 and not in the second half of 1917.  Where have you got it's speed?

 

Thanks!

Edited March 16, 2014 by Bucksnort

[+gavagai]

I don't claim they had French-made Clerget engines.  Some of the license built engines were OK, many of them were not.

 

For airspeed, I would go with what Rise of Flight has.  When they have the time of year for test data, they will adjust performance to match 15 degrees C and 767mm Hg.  They did that for the D.VII and I am confident they did that for the Triplane.  Otherwise it would fly 120+ mph.

[Bletchley]

Loss of power in Clerget rotaries was mainly due to loss of compression from worn or badly fitting obturator rings - these needed replacing very frequently (about every 15 hours, if I recall correctly). Those made by Clerget appear to have been better engineered, and suffered less from this loss of compression, than those engines made under licence in France or England. Ruston & Procter (RP) made steam traction engines before the war, and built Clerget engines under licence for the RFC. Despite their lack of previous aero-engineering experience, their engines appear to have been better than those made by Gwynnes for the Admiralty (Gwynnes made marine pumps before the war). Gwynnes made both the 7Z and the 9B, and their reliability was so poor that Bentley was sent by the Admiralty to 'sort them out'. Amongst other improvements, he managed to persuade Gwynnes to replace the original Clerget cast iron pistons with aluminium alloy pistons, which dispensed with the need for obturator rings (as the aluminium alloy was better at distributing the heat). After Bentley had left to work on his BR1, Gwynnes worked with Clerget engineers to produce the 9Bf that also used aluminium alloy pistons (which also had no need for the obturator rings). The 'good' Gwynnes Clerget in the above post may have been one of these later ones (at least, the serial number of the a/c is higher). You might find these threads from The Aerodrome forum of interest :)

 

http://www.theaerodrome.com/forum/aircraft/40767-powerplant-sopwith-triplane.html

 

http://www.theaerodrome.com/forum/aircraft/34659-sopwith-camel-f-1-engines-part-1-a.html

 

http://www.theaerodrome.com/forum/aircraft/34660-sopwith-camel-f-1-engines-part-2-a.html

 

B.

[Bletchley]

Edit to above: for 7Z read 9Z!

 

Also, to add - R&P changed from using cast iron pistons to aluminium alloy pistons at about the same time as Gwynnes, I think (as did Le Rhone and most other British aero engine manufacturers), so that might help explain the better performance of the RP a/c with the higher serial no. Also, as you can see, the early AR1/BR1 was not significantly better than the 're-pistoned' Clerget, until later improvements were made to the BR1 (including a higher compression ratio), and the Gwynnes 9Bf was comparable to the later BR1 in output and performance.

[Bletchley]

Edit (again) : the aluminium alloy pistons didn't dispense with the need for obturator rings (the 9Bf still had them).

[Bucksnort]

Hi Bletchley,

 

Thanks for all this info...very interesting. From what I've read, Germany also had problems with premature wear of their rotaries later in the war due to having to use synthetic oil rather than the preferred castor oil for lubrication. So the Dr1 often had less than 110 ponies pulling it around the sky also.

Edited March 27, 2014 by Bucksnort

[+gavagai]

Bucksnort, not sure if you saw this yet from chill31:

 

 

 

I did a four leg speed test of my Dr1 running flat out, full throttle in level flight at 3,600 ft density altitude. I estimate the actual power transmitted to producing thrust at about 105HP which gave me 107 mph

 

That's the only level airspeed gps data we're going to get from a contemporary (replica) Dr.I pilot.  We'll never know the real airspeed of the WW1 Dr.I, but his measurement lines up well with our old hypothesis that it was not as fast as the ~115mph figures that can be found.